Hello
I would appreciate if you could help me to understand the sign criteria for the propagation direction of the waves and wind using the input values WaveDir from HydroDyn module and PropagationDir from Inflowind.
The definitions on the user guides say:
WaveDir is the mean wave propagation heading direction (in degrees), and must be in the range (-180,180].A heading of 0 corresponds to wave propagation in the positive X-axis direction. And a heading of 90 corresponds to wave propagation in the positive Y-axis direction.
PropagationDir: Direction of wind propagation [degrees]. This input parameter is used to rotate the entire wind field for all wind file types. The rotation angle is specified as a meteorological rotation angle about the Zi-axis (rotation from alignment with positive Xi towards negative Yi). This is a clockwise rotation when looking from above towards the surface of the ground or ocean.
I have drawn and attached what I understand from these definitions but I am not sure if I am understanding this sign convention correctly. In the image you will see that both waves and wind rotation is positive in the same direction but I am not sure if wind rotation sign is opposite. Would you mind taking a look at it and confirming if this is correct or not. If not I would appreciate a similar kind of drawing with the correct sign convention.
Many thanks
Gustavo
1 Like
Dear Gustavo,
Your image for the wave propagation direction in HydroDyn (WaveDir) is correct. But your image for the wind propagation direction in InflowWind (PropagationDir) is reversed. WaveDir is defined counter-clockwise when looking from above; PropagationDir is defined clockwise when looking from above.
I hope that helps.
Best regards,
Dear Jason
First, thank for your prompt reply. It is clear now and I can keep on running simulations confidently.
I had the feeling that Wind propagation sign convention was reversed as you mentioned but I was not 100% sure about it. I was wondering why making it opposite to the wave sign convention and that made me doubt.
Best Regards
Gustavo
Dear Gustavo,
The wind propagation direction follows standard meteorological convention, whereas most other FAST inputs/outputs follow the “right-hand rule” for rotation about an axis.
Best regards,
Dear Jason
Thank you for the clarifying this point. It makes complete sense.
Regards
Gustavo
Hello,
I was wondering if someone can please clarify the directions for wind and waves. Is it true that PropagationDir is specified as the direction that the wind is coming from, but WaveDir is the direction that the waves are heading towards?
I understand that the wind direction is specified looking clockwise from above and wave direction is anti-clockwise, but is the 0 degrees direction aligned for both coordinate systems?
Thanks,
Rachael
Dear Rachael,
I would say that PropagationDir in InflowWind defines the wind direction and WaveDir in HydroDyn defines the wave direction, but–as you said, PropagationDir is defined clockwise from above and WaveDir is defined anti-clockwise from above. Zero degrees for both means that the wind and waves propagate along the +X axis of the global inertial frame coordinate system.
Best regards,
Dear Jason,
Thank you for your response. Sorry for the stupid question, but does that mean that if the +X axis is pointing south, then zero degrees for both would mean that the wind and waves are both propagating from north to south?
Thanks,
Rachael
Dear Rachael,
Yes, that is correct. That said, FAST / OpenFAST does not explicitly ues the compass direction, and so, has no knowledge of north/south/east/west.
Best regards,
Dear @Jason.Jonkman
I have some questions about the inflow wind module used in FAST.Farm, I used TurbSim to generate a large-scale wind field(attachment 1 in setting), in order to be able to simulate its inflow from 112.5° (compared to the positive x-axis direction), I modified Some parameters as follows， which could see in attachment2-4:
Inflow Input File parameter - PropagationDir == 112.5,
ServoDyn.dat - YawNect & NacYawF = -112.5,
ElastoDyn.dat - NacYaw = -112.5,
In fact, when I use a wind turbine and a small-scale Farm for testing, the effect is ok. However, when I expand the simulation area of the wind field, it prompts an error “FF wind array boundaries violated: Grid too small in Y direction”
I tried several different grids, but all got various errors, the details are in attachment 5.
Although I consulted the inflow user manual, I am still a bit confused about the transformed area. The original wind field is symmetrical about the y-axis [-4250, 4250]. Is the transformed wind field a rectangular area with PropagationDir as the axis?
I also tried to use inflow_driver for simulation. After opening the WrVtk setting, although the program can run, it seems that the program keeps creating the VTK folder and only writes a Vtp file due to the code. By opening one of the vtp files of the yz plane, The grid of found data is still set like this:
DATASET STRUCTURED_POINTS
DIMENSIONS 1 851 43
ORIGIN 0.00 -4250.00 1.00
SPACING 0.00 10.00 10.00
This makes me very distressed, hope to get your answer and help.
Best Regards,
Jundong Wang
Attachment setting
Dear @Jundong.Wang,
I haven’t reviewed the files you’ve shared, but the FAST.Farm modeling guidance (4.2.15.6. Modeling Guidance — OpenFAST v3.3.0 documentation) recommends that you align the grids from the TurbSim wind domain and the low- and high-resolution domains in FAST.Farm. This is only really possible when setting PropagationDir = 0, +/-90, or 180 degrees, as mentioned in the FAST.Farm documentation. I would generally recommend setting PropagationDir = 0 in InflowWind when running FAST.Farm. To simulate different wind directions, it is better to rotate the wind turbines and wind farm rather than rotating the wind propagation direction.
Best regards,
Dear @Jason.Jonkman
I successfully adjusted the inflow wind of the onshore wind farm，
Inflow Input File parameter - PropagationDir == 90,
ServoDyn.dat - YawNect & NacYawF = -90,
ElastoDyn.dat - NacYaw = -90,
I would like to know, if I want to do the same adjustment for the OC4 wind farm, do I need to adjust the platform angle in addition to the above parameters and wave propagation direction?
When I did not adjust the wave angle, I received an error message Ct>2.0
Later on, I simply adjusted the direction of wave propagation
WaveDir = -90
But the error is as follows：
HydroDyn_Init:WAMIT2_Init:DiffQTF_InitCalc: Minimum wave direction required of -90 is notfound in
the WAMIT data file ./OpenFAST/5MW_OC4Semi_WSt_WavesWN/../5MW_Baseline/HydroData/marin_semi.12d
for the first wave direction.
DiffQTF_InitCalc: Minimum wave direction required of -90 is notfound in the WAMIT data file
./OpenFAST/5MW_OC4Semi_WSt_WavesWN/../5MW_Baseline/HydroData/marin_semi.12d for the second wave
direction.
T2:Farm_InitFAST:FWrap_Init:FAST_InitializeAll:HydroDyn_Init:Waves_Init:VariousWaves_Init: The
random number generator in use differs from the original code provided by NREL. This pRNG uses 8
seeds instead of the 2 in the HydroDyn input file.
H
Aborting FAST.Farm.
May I know how to adjust it?
Dear @Jundong.Wang,
If you want to simulate different wave directions relative to the floater, you can either rotate the wave direction or rotate the FOWT. If you change the wave direction while using the potential-flow solution, your potential-flow hydrodynamic data must encompass the wave directions you are setting. For the OC4-DeepCwind semisubmersible, we have only generated the second-order potential-flow solution for a single (zero-degree) wave direction, due to the computational expense of generating the second-order potential-flow solution in WAMIT. So, for this model, you’ll have to either keep the wave direction at zero, disable second-order potential-flow effects, or run WAMIT (or equivalent) to generate the second-order solution for other wave directions.
Best regards,
Dear @Jason.Jonkman
Thank you for your very quick response. I will try using the WAMIT method you mentioned, but now I want to make a result first
As I mentioned earlier, I have already set some parameters regarding the angle. I would like to know if it is necessary to modify PtfmYaw?
Best regards,
Dear @Jundong.Wang,
Considering that platform yaw is limited in ElastoDyn to moderate angles (up to about 15-20 degrees before accuracy is lost), I would not suggest using PtfmYaw for different floater orientations.
Best regards,
@Jason.Jonkman
I got it!
Thanks for your suggestion.
Best regards,
Dear @Jason.Jonkman,
I am trying to simulate different wind directions in FAST.Farm, so as you suggested I should rotate the turbines and wind farm while keeping PropagationDir = 0. My question is, what are the parameters that allow me to rotate the platform of the single wind turbine? I ask because I have not found anything in the literature.
Kind regards,
Marco
Dear @Marco.DePascali,
A similar question was recently asked and answered in the discussions section of the OpenFAST GitHub repository: Rotating Ptfm orientation for FAST.Farm · OpenFAST/openfast · Discussion #1902 · GitHub.
Best regards,
Dear @Jason.Jonkman ,
Thanks for the recommendation, your response to @MYMahfouz helped me a lot but I am still missing something, so to remove any doubt on this topic, I would like to ask you a little more detailed question.
If I want to simulate a case where in a wind farm the wind is coming from +10deg (according to the Inflow convention: “Wind propagation direction (meteorological rotation from aligned with X (positive rotates to -Y) – degrees)”) with the rotor plane placed orthogonally to the wind direction, and with the wave direction aligned to the wind direction, I should:
- keep “PropagationDir” equal to 0deg;
- set “PtfmRefzRot” = +10deg to rotate WAMIT data (Aij, Bij, Cij, Xi) from local WAMIT coordinates to global OpenFAST coordinates;
- keep “WaveDir” equal to 0deg;
- rotate the positions of the fairlead /anchors in the mooring module by +10deg.
- Rotate the joints in the Morison element (as well as the joints in SubDyn, if enabled);
In this regard a small question: in the case below (IEA-15-RWT-UMaineSemi), the coordinates of the joints are (0,0,-30.1) and (0,0,15) (see attachment). Having to apply a rotation along the z-axis should not change anything in these coordinates, right?
- Keep “NacYaw” equal to 0deg.
I apologize for the challenging question, but I would like to fully understand the procedure required to rotate the turbine.
Thank you very much
Marco
Dear @Marco.DePascali,
I agree with all of your points.
Best regards,
